gh-90473: WASI: skip gethostname tests (GH-93092)

- WASI's ``gethostname()`` is a stub that always fails with OSError
  ``ENOTSUP``
- skip mailcap ``test`` if subprocess is not available
- WASI process_time clock does not work.
(cherry picked from commit 760ec8940a)

Co-authored-by: Christian Heimes <christian@python.org>

Lib/test/test_support.py

@@ -664,6 +664,7 @@ def id(self):
             self.assertTrue(support.match_test(test_chdir))
 
     @unittest.skipIf(support.is_emscripten, "Unstable in Emscripten")
+    @unittest.skipIf(support.is_wasi, "Unavailable on WASI")
     def test_fd_count(self):
         # We cannot test the absolute value of fd_count(): on old Linux
         # kernel or glibc versions, os.urandom() keeps a FD open on